The invention described herein may be made, used, or licensed by or for the U.S. Government for U.S. Government purposes.
Heretofore, the generation of clean signals in the acoustic range of 6-20 Hz. has not been attainable by any of the commercially known systems. Thus, for example, systems employed for generating power in the audible acoustic range as described herein have operated on different physical principles. For example, a typical commercial product known as a hydrosonic subwoofer is disclosed in U.S. Pat. No. 5,281,777. This device includes a fluid damped acoustic enclosure system for a loudspeaker having an enclosure which defines first and second chambers separated by a common wall in which a loudspeaker is sealably mounted. In the operation of the device, a flexible bladder is filled with a fluid and maintained in the first chamber a given distance above the loudspeaker. The flexible bladder receives acoustic pressure waves generated by the loudspeaker. The bladder is mechanically coupled to a portion of at least one wall of the first chamber that communicates with the exterior of tie enclosure.
In this prior art system, the fluid damped enclosure system causes bags of water and a flexible wall to vibrate mechanically at low frequency. In this manner, sound waves are coupled to relatively rigid radiating surfaces and, simultaneously, a portion of each pressure wave is reflected back toward its source, so causing a reflective damping system.
A review of this system reveals that it is a driven damped harmonic oscillator system wherein bags of water and a flexible plate and their boundary containment evidence a spring constant and damping factor.
An alternative system comprises a large mechanical piston that adiabatically compresses, air in a room without any concept of resonance.
This invention relates to an infrasonic sound power source. More specifically, the present invention relates to a portable, efficient power source of infrasonic sound within the range of 6-20 Hz, without generating spurious frequencies, using a Helmholtz resonator.